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Peabody Museum
of Natural History
Yale University
New Haven, CT 06511
Postilla
Number 189
29 July 1983
Osteology and
Functional Morphology
of Dimorphodon macronyx
(Buckland) (Pterosauria:
Rhamphorhynchoidea)
Based on New Material
in the Yale Peabody Museum
Kevin Radian
(Received 18 February 1982)
Abstract
Two incompfete skeletons and other isolated bones of Dimorphodon macronyx
(Buckland), an early rhamphorhynchoid pterosaur from the Lower Lias (Hettangian) of
England, have remained undescribed in the
collections of the Peabody Museum of
Natural History since their acquisition by 0.
C. Marsh over a century ago. Some of this
material comes from Aust Cliff near Bristol,
and therefore constitutes the first record of
Dimorphodon outside the Lyme Regis area
of Dorset. The two individuals are smaller
than those in the British Museum (Natural
History) described by Owen, and juvenile
proportions characterize both cranial and
postcranial remains. Much of the material is
three-dimensional and has been prepared
from its matrix; it provides some of the
fullest structural and functional information
available for any pterosaur. A particularly
well-preserved humerus gives insight into
the articulations and folding of the wing,
and two sets of distal tarsals demonstrate
the mesotarsal flexion of the ankle. Comparison with more extensive but less fully
prepared material in the British Museum
(Natural History) allows some osteological
identifications to be established or
corrected; it also provides the basis for a
new assessment of structure and function
in pterosaurs. The forelimbs could not have
moved parasagittal^ but were well suited
for an active flight stroke. The hindlimbs
were positioned and moved like those of
bipedal dinosaurs and birds. The feet were
digitigrade and were not adapted to hang
from trees or cliffs. Comparative osteology
indicates that these features and abilities
conform very well to an "advanced archosaurian" Bauplan seen in dinosaurs and
birds.
Key Words
Pterosauria, functional morphology,
Dimorphodon, Archosauria.
Abbreviations
® Copyright 1983 by the Peabody Museum of Natural History, Yale University. All rights reserved. No
part of this publication, except brief quotations for
scholarly purposes, may be reproduced without the
written permission of the Director, Peabody
Museum of Natural History.
The following institutions are referred to in
the text:
BMNH British Museum of Natural History
(London)
YPM
Peabody Museum of Natural
History, Yale University
2
Dimorphodon macronyx
New Material
(Buckland)
Introduction
0. C. Marsh was the first American paleontologist to write extensively on pterosaurs.
He did most of this work in the 1870s, concentrating on the giant Cretaceous pterodactyloids of the western United States. By
1872 he had already found enough material
to name two new species, Pterodactylus
ingensand Ft occidentalis. In 1876 he
separated these and several other new
large American forms into two new genera,
Pteranodon and Nyctosaurus, and named
a new suborder of the Pterosauria
(Pteranodontia). These strange forms with
their bizarre crests were larger than any European finds, and their discovery attracted
worldwide attention. In his publications
over the remainder of the decade, Marsh
wrote on the general characters of Cretaceous pterosaurs, and also described the
first record of a Jurassic pterosaur from
North America, Pterodactylus montanus
(1878), from the Morrison Formation; he
changed its name to Dermodacty/us in
1881. In 1884 he began a description of the
skull of Pteranodon, but this work was left
unfinished. The study of American pterosaurs was later taken up by Williston, who
began in the 1880s, and by Eaton (1910),
who resumed work on the Yale Pteranodon
material after Marsh's death in 1899.
Marsh did not confine his research to
American pterosaurs, although his efforts
with European forms were less successful.
In 1873, he made two purchases of European pterosaur material for the Yale College
Museum. One was the fine specimen of
Rhamphorhynchus phy/Iurus from the
Upper Jurassic of Bavaria, the first pterosaur to be discovered with impressions of
the wings still intact. The circumstances of
its acquisition have been described by
Schuchert and LeVene (1940). The second
European pterosaur was Dimorphodon
macronyx, from the Lower Lias of Lyme
Regis, Dorsetshire, which Marsh purchased
from the fossil shop of Bryce M. Wright in
London. Despite the value of this European
material, however, Marsh postponed work
Postilla189
on it. He did not publish his description of
Rhamphorhynchus phyllurus until 1882,
claiming "I'embarras de richesses nearer
home," and when he finally did, his study
was only cursory. The Dimorphodon material was never described.
The aim of the present work is to describe the material, which has remained in
the Yale collections for a hundred years.
Dimorphodon has not been studied extensively since 1870, when Sir Richard Owen
described the material in the collections of
the British Museum (Natural History).
Owen's evolutionary beliefs greatly colored
his choice of anatomical comparisons and
his conclusions about the functional
morphology and physiology of
Dimorphodon. His description brought
strong objections in the form of a detailed
reply from H. G. Seeley (1870), who challenged nearly every aspect of Owen's
monograph (Padian 1980). The resulting
confusion still needs clarification, and
recent discoveries have provided much
better evidence on which these questions
can be assessed.
Historical Background and Inventory of
the Material
The specimens in the Yale collections
referred to Dimorphodon were acquired in
three accession lots. All of them were
bought from the shop of the fossil dealer
Bryce M. Wright, 90 Great Russell Street,
Bloomsbury, London, probably between
1873 and 1882. The accession numbers in
the Yale catalogue are 456,462, and 1503.
It is difficult to learn much about the
histories of these specimens. The material
was not collected systematically, and the
locality datum "Lyme Regis" is probably
general, like the usual designation of
"Solnhofen" for much of the pterosaur
material from the Upper Jurassic of Bavaria.
It is unlikely that most of the Dimorphodon
material was collected far from Lyme Regis
itself, but the fossiliferous localities there
extend for several miles, and are dozens of
3
New Material
(Buckland)
meters thick in places. Beyond this, there is
the problem of correlating Wright's own
catalogue numbers with the numbers on
his packing lists. In a letter to Marsh dated
21 June 1873, Wright expresses regret that
Marsh has found some of the unsolicited
material sent him unsatisfactory, and adds,
"I will not forget to procure if possible the
pterodactyle remains and other of your
desiderata and will confine myself solely to
those specimens you desire." But we do not
know exactly what Marsh returned to
Wright and how it may have affected inventory listings. It is unlikely that he sent back
anything pterosaurian, because Wright
refers to Marsh's requests for pterosaur
material in at least twelve letters. He is
always reminding Marsh of how scarce it
is, but promising to send whatever he can.
Thirty letters from Wright to Marsh, covering the years 1871-77, are preserved in the
Yale University Archives (Series I, Box 36,
Folder 1556), but unfortunately we do not
have Marsh's letters to Wright.
Lot 456 is inventoried in a packing list
from Bryce Wright dated 21 March 1873. It
includes 87 separate items, for which
Marsh paid a total of £ 91. The first item
on the list is the pterosaur material, which
consists of a slab and several smaller
pieces. Wright listed it as follows: "No. 1.
Humerus, ulna, and radius, etc., of pterodactyle in case and wing bones— 1 rib and
1 other. Lias. £ 5.10.0." Wright evidently
meant the main slab when he said "in
case," which leaves the "wing bones, 1 rib
and 1 other." Four other small pieces of
Lyme Regis matrix also have the accession
number 456 and "No. 1" on their labels.
Two are isolated wing bones, another is the
rib, and the fourth, labeled simply "bone of
Dimorphodon... "is the distal end of a
right humerus.
Two other pterosaur bones from Lyme
Regis have the accession number 456. One
is a shattered third wing-phalanx labeled
"No. 26" on the back of the slab. This
number does not correspond to Wright's
listing in his letter of 21 March 1873 (No. 26
on his list is "Head and jaw of Belenos-
Postilla189
tomus anningiae"), but it may have been a
misprint of a number in Wright's catalogue.
There is also a left wing-metacarpal, which
has been prepared from its matrix. It is
identified by a label that corresponds to
Wright's No. 81 in the list for lot 456, which
reads simply "bone of pterodactyle."
Lot 462 is inventoried in a letter from
Wright to Marsh dated 29 May 1873. This
lot contains 37 items, including material of
cave bear, plesiosaurs, turtles, mosasaurs,
and many other vertebrates, for which
Marsh paid £ 76.15.6. One piece of bone
is labeled "No. 27. Pterodactyle bone, Lyme
Regis," and is evidently the distal end of
another right humerus. The No. 27 on
Wright's packing list does not correspond
to pterosaurian material; however, his No.
26 does.
The third accession lot (1503) containing
Dimorphodon material is represented by a
slab of black limestone (commonly called
"Blue Lias") with fragmentary cranial and
postcranial remains. The label is Wright's
stationery, but the handwriting may be
Marsh's; the locality given on the label is
"Lyme Regis, Dorset, England." Accession
number 1503 was received 16 September
1881 and contains European fossils donated by Marsh, probably received or bought
by him during his European trip of that year
(Marsh 1881b). The material is listed in only
two parts in the accessions catalogue: "(a)
casts of monkeys from Prof. A. Gaudry,
Jardin-des-Plantes, Paris," and "(b) Tertiary
fossils from Prof. A. Julien, ClermontFerrand, France." However, under entry
1503 in the original receipt book from
which the listings in the accessions catalogue had been copied, there are not two
items, but five. The first two correspond to
(a) and (b); the last two include various
fossils bought in Germany, but the third
reads "(c) slab of Bone Bed rock from Aust
Cliff, Gloucester, England, bought of B. M.
Wright, London."
How can the discrepancy in locality data
be explained? All the known material of
Dimorphodon comes from the cliffs of
Lyme Regis, Dorset, on the southern shore
4
New Material
(Buckland)
Fig. 1
Map of the southwest of England and Wales,
with Lower Liassic horizons stippled. Based on
1958 Ordnance Survey Map of Great Britain.
Postilla 189
5
New Material
(Buckland)
of England; the first two specimens were
collected by Mary Anning. Aust Cliff is not
in Dorset, but in Gloucester, on the south
bank of the River Severn (Fig. 1). However, a
thin outcrop of Liassic deposits runs north
from Dorset to the region of Aust, and the
top of Aust Cliff consists of three feet of
Lower Lias (Geological Survey of Great
Britain, Map 250, Scale 1:63660,1958).
Beneath this is 25 feet 6 inches of Rhaetic,
22 feet 9 inches of "Tea Green Marl" (Upper
Keuper), and 97 feet of red marl. The black
limestone slab is typical "Blue Lias," so it
could indeed have been collected from the
top of Aust Cliff—although not from the
"Bone Bed" of Aust Cliff listed in the YPM receipt book, because the latter is a light conglomerate of basal Rhaetic age, much
lower in the section (Reynolds 1947). This
specimen therefore marks the first occurrence of a Lower Liassic (Hettangian) pterosaur from a region in England other than
Dorset.
In Table 1 all YPM specimens referred to
Dimorphodon have been tabulated and
identified, and their principal measurements given. The only part of the
K
M
Postilla189
Dimorphodon material to receive a Yale
Peabody Museum catalogue number was
the main slab of accession lot 456, which
was catalogued as YPM 350 in 1927. This
included a right humerus (YPM 350 F), a
right lateral carpal (YPM 350 H), two metacarpals of the series l-lll (YPM 350 A and L),
two phalanges from the manus (YPM 350 E
and J), a pair of contiguous second and
third wing-phalanges (YPM 350 D and 0 ,
and what may be part of a fourth (YPM 350
K). Of the hindlimb there is preserved the
complete right tibia-fibula (YPM 350 B),
two distal tarsal elements (YPM 350 M and
R), metatarsals ll-IVof the right pes (YPM
350 P), metatarsals III and IV of the left pes
(YPM 3501), and two pedal phalanges
(YPM 350 G and N). All of these have been
removed from the slab (Fig. 2), and except
for the fragile long bones (YPM 350 B, C,
and D), are completely free of matrix.
Fig. 2 •
Dimorphodon macronyx (Buckland), YPM 350,
slab showing presumed original positions of
the bones, which have been removed from the
matrix. Restored from photographs; dimensions approximate. For identification and measurements of lettered elements, see Table 1.
6
New Material
(Buckland)
Postilla189
Table 1
Inventory and Measurements (in mm) of YPM Dimorphodon Material
Item Description
Accession Number 456: YPM 350
(Bryce M. Wright's "No. 1" of 21 March 1873)
350 A
Metacarpal
350 B Right tibia-fibula
350 C Third wing-phalanx
350 D Second wing-phalanx
350 E Phalanx of right manus
350 F Right humerus
350 G Phalanx of pes
350 H Right lateral carpal
350 I
Metatarsals III and IV of left pes
350 J
350 K
350
350
350
350
L
M
N
P
Phalanx of right manus
?partial fourth wing-phalanx
or phalanx of fifth toe
Metacarpal
Left lateral distal tarsal
Phalanx of pes
Metatarsals ll-IV of right pes
Median
Width
Width
Prox. End
30
104
105
97
78
10
6
4
9.5
7
9
3.5
29
2.5
—
2.5
6.5
6.5
7.5
3
17
2
—
1.5
1.5
5
4
2
5-6
0.9
5
inc
7
3.5
2.8
2.5
1.2
1.2
(23.5)
(2.5)
(1.8)
(1.0)
32
6
7
4
—
2
3
—
1.5
1
2
1
32
2
1.5
1.5
—
9
2
2
2
—
1
1.2
1.2
1.2
4
2
70
8.5
4
(7)
4
4
3.5
(31)
-
10.5
4
107
4
4
3
36
12.5
8
5
10.5
32.5
IV
350 R Left medial distal tarsal
YPM 9175
Rib ("No. 1")
YPM 9176
Second wing-phalanx
("No.1")
YPM 9177
?Ulna("No. 1")
YPM 9178
Distal end of right
humerus ("No. 1")
YPM 9179
Third wing-phalanx
("No. 26"?)
YPM 9180
Leftwing-metacarpal
("No. 81")
(Bryce Wright, 29 May 1873, No. 26 or 27
YPM 9181
Distal end of right
humerus
(Bryce Wright, 16 September 1881)
9182 A Left maxillary and jugal
9182 B Upper jaw fragment
9182 C Right humerus
9182 D Distal end of first
wing-phalanx
9182 E Second wing-phalanx
9182 F Left femur, missing
proximal end
9182 G Right femur
9182 H Right tibia-fibula
9182 I Fused right distal tarsals
9182 J Metatarsal
9182 K Unidentified shaft fragment
nearB
Width
Dist. End
Length
32
4
40
(78)
12
37
—
—
87
23
63
21.5
18
74
7
(50)
59
85
6
(22)
45
11.5
8
—
1.8
10
—
—
15
4-5
8
(crushed)
7.5
6
5.5
3.5
9
8
5.5
—
—
5
4.5
4
4
0.8
6
8
7
New Material
(Buckland)
The other material under lot 456 has
been left uncatalogued until now. Of these
specimens, the rib listed under "No. 1" has
been designated YPM 9175; the nearly
complete wing-phalanx is YPM 9176; the
presumed ulna is YPM 9177; and the distal
end of the right humerus is YPM 9178. All
of this material and the main slab represent
Wright's "No. 1" on his original list. "No. 27"
on his list ("No. 26" on the specimen label)
is the shattered third wing-phalanx, now
numbered YPM 9179; the isolated left
wing-metacarpal ("No. 81") is YPM 9180.
The partial bone from lot 462, evidently a
distal end of another right humerus, has
been given YPM 9181.
All the material on the slab from Aust
Cliff (accession number 1503) is now YPM
9182. The slab of matrix is in the shape of a
rough trapezoid measuring about 25 cm
along the base, 8 cm along the top, 32 cm
in height, and 2.5-4 cm in thickness (Fig. 3).
The Dimorphodon material includes two
dentigerous parts of the upper jaws, the
right humerus, the left femur (without the
proximal portion: Fig. 4c), the complete
right femur, the right tibia-fibula, the distal
end of a first wing-phalanx, the entire
second wing-phalanx adjacent to it, two
contiguous distal tarsal elements, a single
metatarsal, a possible fragment of the
radius and ulna, and a small bone scrap,
probably the hemicentrum of a fish. Of
these bones, the humerus, right femur
and tibia-fibula, first and second wingphalanges, and tarsals have been prepared
out of the matrix. All bones are typically
crushed flat and, except for the humerus,
afford little three-dimensional relief.
Description
The osteology of pterosaurs has been well
known for over 120 years, due largely to the
many works of Hermann von Meyer, who
concentrated his research on the Upper
Jurassic forms of Bavaria. The discoveries
and advances of the following century
made necessary an extensive anatomical
Postilla189
and systematic revision of the Pterosauria,
which has been expertly carried out by
Wellnhofer (1970,1974,1975,1978). The
recent discoveries of pterosaurs in the
Triassic of Italy (Zambelli 1973) and their
detailed descriptions (Wild 1978) have also
contributed greatly to an understanding of
the anatomy and diversity of the earliest
members of this group. The purpose of the
present work, accordingly, is not to provide
detailed analysis of pterosaurian osteology,
but to point out those features in the Yale
specimens that cast new light on an important early pterosaur and on the functional
mechanics of pterosaurs in general.
Skull
Two fragments of the upper jaws are preserved in YPM 9182. The smaller (Fig. 4b) is
from the right maxilla, seen in lateral view.
It is 19 mm long and 4.5-8.0 mm high, and
bears three slightly recurved, sharply pointed teeth approximately 6 mm apart. The
shape of this fragment and the size of its
teeth appear to correspond to a part of the
other fragment of the jaw preserved on the
slab. Neither piece contains either the very
enlarged laniaries found in the premaxilla
and foremost part of the dentary, nor the
minute "lancet-shaped" teeth found along
most of the dentary, for which Dimorphodon was named.
The second fragment (Fig. 4a) is larger
than the first. It consists of most of the
lower border of the left side of the skull,
seen in lateral view, including nearly the
entire maxillary bone and most of the jugal.
In Dimorphodon the orbit sits higher in the
skull than both the preorbital opening and
the nares. The lower border of the orbit is
formed by the upper edge of the jugal
bone; the middle ascending process of the
jugal separates the orbit from the preorbital
opening. This process is incomplete in YPM
9182, but its configuration is clear. The
entire lower border of the preorbital opening is outlined; it is approximately 33 mm
at its widest point. A small thin flange of
bone protrudes anteriorly at a low angle
8
New Material
(Buckland)
PostiIla189
^%-±<$%y^ ri i
*?
-'^
r
^
*•
9
New Material
(Buckland)
from the lower border of the preorbital
opening. This may be the thin lateral flange
of the pterygoid, which articulates with the
ectopterygoid in the region just medial to
the jugal in Campylognathoidesand
Rhamphorhynchus (Wellnhofer 1974;
1978, Abb. 3).
The suture between the jugal and
maxilla, like most skull connections in
pterosaurs, is unclear. Owen (1870) did not
even identify a jugal bone in his description.
Von Meyer, the 19th-century German
authority on pterosaurs, succinctly summarized the problem in Zur Fauna der Vorwelt
(1859:15, translated by Seeley 1870).
In Pterodactyles, as in birds, the bones of
the skull blend together so imperceptibly
that their sutures at best are only indistinctly seen, and are sometimes obliterated;
while even in full-grown reptiles they are
all to be made out with great distinctness.
There is the more difficulty in ascertaining
the structure of the Pterodactyle skull,
since generally only the lateral aspect is
exposed, and hence we get scarcely any information about its upper and under
surfaces. Among the skulls which are exposed from the side, information is at times
afforded by those in which the parts have
suffered some displacement; but the separations so produced are to be accepted
with great caution, for they do not always
coincide with the real boundaries of the
bones.
Pterosaur bone is so delicate that it is
easily checked and shattered. There are at
least four different reconstructions of the
< Fig. 3
Dimorphodon macronyx, YPM 9182, slab.
Abbreviations: fv, hemicentrum of a fish, possibly Pholidophorus; If, left femur; / uj, left
upper jaw; mt, metatarsal; f r i g h t femur;
rhum, right humerus; rt, right distal tarsals;
rt-f, right tibia-fibula; ? r-u, possible portion of
a radius and ulna; ruj, right upper jaw; wph 1,
first wing-phalanx; wph 2, second wingphalanx. Scale in mm; measurements given in
Table 1.
Postilla189
skull of Dimorphodon, all drawn from the
same specimen, and all with different interpretations of sutural connections (Fig. 5;
see also Seeley 1901 and von Huene 1914).
Figure 6 illustrates the portion of the skull
of Dimorphodon represented by YPM
9182, based on the skulls in the British
Museum (Natural History), described by
Owen (1870). There is no clear connection
between the maxilla and premaxilla, but
bearing in mind von Meyer's cautionary
remarks, the approximate extent of the
nares may be inferred from the basal length
of the preorbital opening. The fragment of
bone preserved here ends at a point just
short of the hypothetical anterior limit of
the nares. This is the case for most
rhamphorhynchoids, as Wellnhofer (1978,
Abb. 2) shows. The usual reconstruction of
this suture in Dimorphodon differs from
the rhamphorhynchoid pattern (Fig. 5), but
the evidence for this is not clear. It seems
equally possible that the anterior end of the
Yale specimen represents the natural break
between maxilla and premaxilla. Seven
maxillary teeth are preserved, and there are
alveoli for one or two more; this corresponds to Owen's assignment of eight or
nine teeth to the maxilla. The premaxilla,
bearing the four large laniaries, would form
the snout and the anterodorsal border of
the nares, as in other rhamphorhynchoids
(Wellnhofer 1978, Abb. 2). As no evidence
of a large alveolus for the fourth laniary is
preserved, no portion of the premaxilla appears to be represented in this specimen.
The size and proportions of these cranial
remains imply that the specimen is a
juvenile; this assessment is further supported by the dimensions of the hindlimb,
which will be discussed below.
Dentition
Three teeth have been preserved in the
smaller jaw fragment of YPM 9182, and
seven in the larger. Although none of the
teeth in the larger fragment is complete,
they are clearly the same size as the three
teeth in the smaller fragment, as deter-
10 Dimorphodon macronyx
New Material
(Buckland)
Postiiia189
a
'fifr*.: *->'
-ft? V
in
•-.••.. I
VI * "
:* -
>J& '*'
*_. /S
.;<?
-. .- • ' - • - ^ ^ • ' • ^ ^ H ^ ^ - ^ ^ .S^s&t'*
f\
11
Dimorphodon
macronyx
New Material
(Buckland)
Fig. 4
Dimorphodon macronyx. a, YPM 9182, detail
of slab, showing left maxilla and part of jugal.
b, detail of the same slab, showing dentigerous
part of right maxilla and possible radius-ulna
fragment. Scale is in mm. c, detail of the same
slab, showing isolated metatarsal, e, YPM
9175, rib. Scale bars = 1 cm.
Postilla 189
Fig. 5 T
Four restorations of the skull of Dimorphodon
macronyx. A, Owen 1870; B, Arthaber 1919;
C Wellnhofer 1978; D. Wiman 1923. Parenthetical symbols in A represent Owen's
terminology. Abbreviations: al, adlacrimal; ang, angular; ar, articular; C/, dentary; f,
frontal;/jugal; /, lacrimal; m, maxilla;
/7?/,malar; ms, mastoid; a nasal; p, parietal;
pm, premaxillary; pf, pof, postfrontal; po,
postorbital; poc, pa rocci pita I; prf, prefrontal;
q, quadrate; g/quadratojugal; sa,surangular;
so, supraorbital; spl, splenial; so/, squamosal;
tym, tympanic. Length of reconstructed skull
about 20 cm.
sq(ms)
(sq)
•q(tym)
ang
^Fig.6
Tentative restoration of the skull of the small
and presumed juvenile Dimorphodon
macronyx, based on skull fragment of YPM
9182. Abbreviations as in Figure 5. Length of
reconstructed skull about 14 cm.
New Material
(Buckland)
mined from the size of their roots. The
placement of these teeth along the upper
jaw permits an approximation of the dental
configuration of the juvenile Dimorphodon.
The adult has four large laniaries widely
spaced at the front of the jaw, corresponding to the premaxilla. The maxilla bears
seven or eight smaller teeth of this form, according to Owen (1870), although Arthaber
(1922) figured nine in his reconstruction
(Fig. 5B). The upper jaw fragment described
here has fragments of seven teeth, of which
the last two are very close together. There
is a crushed alveolus midway between the
third and fourth teeth preserved here, and
also a large space (possibly an alveolus)
just in front of the first tooth. This tooth is
not quite parallel to the others, and it may
have been dislodged; the space that separates it from the second tooth is smaller
than in most of the series. This region of the
maxilla is also badly preserved in the other
Dimorphodon skulls. I regard the effective
number of maxillary teeth at this growth
stage to be eight, including the last two,
which are smaller and more closely spaced.
Additional teeth seem to have been formed
at the back of the jaw, and were progressively smaller than those in front.
The most complete teeth are in the smaller jaw fragment. The best preserved of
these is partly disengaged from its natural
position in the alveolus, and all but the tip
of the root is visible. From comparison with
the complete root portions of other teeth,
the entire length of this tooth was approximately 7.0 mm. The form is identical to that
of the larger laniaries, only proportionately
smaller, as the isolated teeth figured by
Owen (1870, plates XVII and XVIII) show.
Owen described the large premaxillary
laniaries as "subcompressed, subrecurved,
and sharp-pointed" (p. 43), with the maxillary laniaries becoming gradually smaller
and less curved towards the back of the
maxilla. The size and shape of the three
teeth in this smaller jaw fragment thus
show that it belongs to the fore or middle
part of the right maxilla. In the lower jaw of
Dimorphodon, which is deeper than this
Postilla 189
fragment, there are three rather large laniaries in the front, followed posteriorly by only
two of the size of the maxillary teeth, and
finally by a long row of "small, lancetshaped, close-set teeth" (Owen 1870:42). It
is therefore likely that this fragment belongs
to the lower jaw, unless the relative size of
some of the teeth changed during growth
and replacement.
Postcranial Material
As frequently happens with disarticulated
pterosaur skeletons, there are no remains of
the pectoral or pelvic girdles or of any vertebrae among the Yale Dimorphodon
specimens; almost all preserved material is
of long bones. A single rib (YPM 9175; Fig.
4e) has been preserved and is tentatively
referred to this taxon. It is double-headed,
wide at the proximal end between the two
heads, which are separated by 9 mm, and
slender along its length (40 mm). A hollow
channel in the proximal part of the shaft between the heads is revealed by crushing of
the surface bone. There is a slight curvature
at the proximal end, but the shaft is quite
straight for 80% of its length. The distal end
is slightly expanded and rounded.
Two complete humeri are preserved.
One right humerus (YPM 9182 C; Fig. 7c)
measures 63 mm from the saddle-shaped
articular surface of the head to the tip of the
ulnar condyle. The proximal articular surface is well preserved and shows the
characteristic lip that articulated with the
glenoid fossa. The natural torsion of the
shaft has been distorted by crushing, but
the deltopectoral crest still preserves some
of its natural curvature. The angle made by
the head and crest of the humerus is slight
when compared to less distorted
specimens, in which the head and crest
may curve anteroventrally to form a semicircular silhouette in proximal view
(Lawson 1975, fig. 1). A bulblike terminal
thickening of the expanded crest has been
preserved; it shows, as Owen (1870:51)
noted, that the deltopectoral crest was not
simply a thin flat plate of bone, as speci-
New Material
(Buckland)
mens often appear to indicate. The distal
end of the humerus is well preserved, particularly the articular condyles for the
radius and ulna, although this area is even
better preserved in the following specimen.
The other complete right humerus (YPM
350 F, Figs. 8 and 3) is exceptionally well
preserved, and its fine condition allows
new insight into the structural and functional details of the forelimb (see Discussion).
The head and neck were separated from
the shaft which itself had been broken in
three places. These portions were all preserved in three dimensions, however, and
were completely repaired. The deltopectoral
Fig. 7
Dimorphodon macronyx, YPM 9182, material
removed from slab, a, second wing-phalanx; b.
distal end of first wing-phalanx; c right
humerus; d. right tibia-fibula in posterior view;
e, right femur.
a
b
c
d
Postillal83
crest was also separated from the main
shaft and slightly crushed in its proximal
area; this portion has proven more difficult
to restore to its original form, and the crest
as repaired has less than the natural
curvature.
The head of the humerus is the typical
saddle-shaped facet with a pronounced
medial lip. A deep notch at the neck separates the lateral {= external or greater) tuberosity from the head of the humerus. The
deltopectoral crest has a pronounced expansion at its distal extremity, as in the
humerus described above and in BMNH
41212. The crest extends nearly 19 mm
from the midline of the shaft, and is
more similar to the narrow form of
Rhamphorhynchus than to the
platelike form of Eudimorphodon and
Campylogna ihoides*
The presence of a pneumatic foramen
cannot be asc :ained because the central
e
New Material
(Buckland)
PostilIa189
v\
i
•v
Fig. 8
Dimorphodon macronyx, YPM 350 F, right
humerus. Head of humerus at upper left, deltapectoral crest at upper right. Scale = 1 cm.
Fig. 9
Dimorphodon macronyx, YPM 350 F, right
humerus. Obverse view of Figure 8. Head of
humerus at upper left, deltopectoral crest at
upper right. Scale = 1 cm.
proximal region of the humerus is fractured
and crushed, but it does not appear to have
been located in the same position as in
birds, A deep channel near the head of the
humerus runs for a short distance parallel
to the axis of the shaft Whether this represents a pneumatic channel is conjectural.
Most perforations taken for pneumatic
foramina have been in uncrushed but worn
and fragmented specimens from the Cambridge Greensand, described by Seeley and
others (see Seeley 1901). Von Meyer,
Owen, and Seeley found pneumatic foramina in many parts of the skeleton, but this
work has not been extensively studied by
later authors, and the whole problem needs
further investigation.
The curvature of the shaft of the
humerus is sigmoid. Seen from the proximal
end, the distal end of the shaft is twisted
nearly 45° posterodorsally (see Fig. 10). Pronounced ridges run along the shaft from
the greater tuberosity to the medial supracondyloid tubercle, and from the edge of
the deltopectoral crest to the lateral supracondyloid process. The paths of these
ridges further outline the torsion of the
shaft and establish the lines indicative of
muscular attachment. They are instrumental in understanding the movement of the
humerus during the flight stroke (see
Discussion).
The distal end of the humerus is well preserved in YPM 9182 C and exceptionally so
in YPM 350 F. The distal condyles and the
adjacent ridges for muscular attachment
are clearly delineated., and Figure 10 points
out some of these comparable features in
New Material
(Buckland)
Dimorphodon and an eagle. In pterosaurs,
as in birds, the radial condyle articulates
with part of the ulna as well as with the
radius, whereas the ulnar condyle articulates only with the ulna. In birds, the main
extensor muscles of the distal segment of
the wing originate from the lateral epicondyle of the humerus, while the principal
flexors of the outer wing originate from the
medial epicondyle (Hudson and Lanzillotti
1955). The comparable development of
these sites of origin in pterosaurs argues for
a similar functional pattern. Two other
distal ends of right humeri are preserved in
the YPM Dimorphodon material (YPM
9178, Fig. 11a; YPM 9181, Fig. 11d), but are
more poorly preserved than the other
humeri and yield no additional information.
YPM 9177 (Fig. 11 e) is a slender, slightly
bowed bone 70 mm long, and is tentatively
identified as an ulna. It is preserved on a
small slab of matrix of which the borders
are encased in cement. A long crack in the
slab, filled with glue, indicates that there
were originally two pieces of matrix. Where
the crack intersects with the bone, a section
of the shaft is missing and has been filled in
with cement. Unfortunately, the cement
that encases the perimeter of the specimen
also abuts against the articular ends of the
bone, making further preparation very
difficult. There is no other diagnostic material of radius or ulna among the Yale
specimens, although an unidentified shaft
fragment 45 mm long, preserved adjacent
to the smaller jaw fragment on the slab of
YPM 9182 (Fig. 4b), may pertain to one of
these bones.
YPM 350 H (Fig. 12a, 13a) is a right lateral carpal. This is a rather robust element
with a concave surface that articulated
with the distal carpal. A convex surface
opposite to this with a round flattened area
supported a small round sesamoid bone on
which the medially directed pteroid bone
rested (Wild 1978, Taf. 9f). Ironically, although this carpal is called "lateral," it is actually located on the medial (radial) side,
and was held in front of the wing when the
wing was outstretched. This medial carpal
Postilla 189
is marked by several tubercles and depressions to which attached the ligaments and
tendons that helped to manipulate the
propatagium. Its form and proportions
correspond closely to those of
Eudimorphodon, Dorygnathus, and
Campylogna thoides.
Two isolated metacarpal bones of the
series l-lll have been preserved (YPM 350 A
and L; Figs. 14c, d; 15c, d). They are extremely delicate and fragile. In comparison
with the metatarsal elements discussed
below, they are thinner and more rounded
in cross-section than the metatarsals of the
same length, and they are slightly bowed in
the lateral direction. Their proximal ends
are widened and flattened into shallowsshaped spatulate surfaces that articulated
with the medial condyle of the proximal
end of the large wing-metacarpal (=mc IV).
Distally the metacarpals expand into round-
Fig. 10 •
Comparisons of the right humeri of the eagle
Aquila (above in each pair)) and Dimorphodon
(below in each pair). A, proximal view, oriented
with the distal ends parallel as in C. Note the
differences in angle of orientation of the heads
and deltopectoral crests. Drawn to the same
size. B, complete humeri in palmar (left) and
anconal (right) views. Scale = 1 cm. C distal
ends in palmar view, drawn to the same size.
/, Processus supracondyloideus lateralis; 2,
Epicondylus lateralis; 3, Trochlea radialis; 4,
Vallis intertrochlearis; 5. Trochlea ulnaris; 6,
Epicondylus medialis; ZTuberculum supracondyloideum mediale; 8, Fovea supratrochl e a r ventralis. dp, deltopectoral crest; gt,
greater tuberosity; h, head; a neck.
Fig. 11 •
Dimorphodon macronyx. a, YPM 9178, distal
end of right humerus; b, YPM 9180, left wingmetacarpal, lateral view; c, YPM 9180, medial
view; d, YPM 9181, probably the distal end of
a right humerus; e, YPM 9177, ?ulna; f, YPM
9176, second wing-phalanx; g, YPM 9179,
shattered third wing-phalanx. Scale bars = 1
cm.
New Material
Fig. 10
bird
pterosaur
pterosaur
(Buckland)
Postilla189
17 Dimorphodon macmnyx
New Material
(Buckland)
Postilla 183
Fig. 11
'**
/
•4.
d
\n
"!ft
ik
*'** <
4
\
''*">£?&
New Material
(Buckland)
ed bulbs with ventral ligamentous grooves;
this expansion was necessary for the reception of the much stouter proximal phalanges of the first three fingers.
Two of these phalanges were preserved
(YPM 350 E and J; Figs. 12c, g; 13c, g).
They are more robust than the corresponding elements of the pes, and their flexor
tubercles are more pronounced. Marked
ginglymal grooves characterize their distal
ends. Viewed from the proximal end, the
flexor tubercles are subtriangular, not
keeled, and distinctly set off to the medial
Fig. 12
Small skeletal elements of Dimorphodon
macronyx, YPM 350, prepared from matrix, a,
350 H. right lateral carpal; b. 350 G. pedal
phalanx; a 350 J, phalanx of right manus; d.
350 R, left medial distal tarsal distal view; e,
350 M, left lateral distal tarsal, distal view; i
350 N, pedal phalanx; g, 350 E, phalanx of
right manus; h, coalesced right distal tarsals of
YPM 9182, distal view; /; YPM 350 K. possible
fragment of fifth pedal phalanx {or fourth wingphalanx?)."Scale = 1 cm.
b
e
d
Postilla189
side. This corresponds to the condition
seen in the first two digits of the dromaeosaur Deinonychus (Ostrom 1989:108). In
both YPM 350 E and 350 J this tubercle is
deflected to the left side, which indicates
that both phalanges belong to the right
manus. They are probably proximal
phalanges, and if so, 350 J probably belongs to digit II, while 350 E may represent
digit III, based on comparison with BMNH
41212. YPM 350 G (Figs. 12b, 13b) is more
slender than these two, and has no
tubercle. It more closely resembles the
proximal phalanges of the pes in BMNH
41212, as does the long gracile element
YPM 380 N (Figs. 12f, 13f), which is incomplete at the dorsal end of its proximal facet
YPM 350 G and N are accordingly assigned
to the hindfoot but cannot be further identified with certainty.
A left wing-metacarpal (YPM 9180; Figs.
11 b, c) 38 mm long is badly crushed and
retains little relief even at its articular ends.
It is a typical broad, flat rhamphorhynchoid
wing-metacarpal, with a well-developed,
laterally placed bicondylar joint at the distal
end, on which the enormous wing-finger
e
f
g
New Material
(Buckland)
pivoted. This isolated metacarpal is 4 mm
longer than the two medial ones catalogued
as YPM 350 A and L White it is unlikely
that it came from the same animal, the discrepancy in size is not great Gallon's
(1381 b) recent description of a superb
rhamphorhynchoid wing-metacarpal from
the Morrison Formation of Wyoming obviates further discussion of YPM 3180 since,
although the relative proportions of this
bone in rhamphorhynchoids are variable,
there are no morphological features diagnostic below the subordtnal level
The distal end of the first phalanx of the
wing-finger (YPM 3182 D), and the complete length of the second phalanx (YPM
3182 E; 74 mm), were preserved in contiguity (Pigs. 3,7a, 7b). The identification of
these wing elements can be made on the
basis of several features, In Dimorphodon
the second wing-phalanx is shorter m
Fig. 13
Obverse views of the same elements of Figure
12, minus /(350 K). Scale = 1 cm.
h
Postilla189
length and broader in cross-section than
the third. The distal expansion of YPM 3182
E is too wide for the reception of the proximal end of the fourth phalanx, when compared to this element in other specimens of
Dimorphodon and in other pterosaurs. The
ratios of the various bones of the wing to
each other (except the metacarpal and the
terminal phalanx) are diagnostic, at least to
the generic level (Padian and Wild, unpublished data). In the two British Museum
specimens of Dimorphodon (BMNH 41212
and R 1035), the length ratios of the second
wing-phalanx to the humerus are 1.38 and
1.23; in YPM 350 C and F this ratio is 1.20,
These specimens have been ranked in decreasing order of size (the second phalanges are respectively 124,102, and 37
mm), and it can be seen that the ratio decreases with growth. In YPM 3182, the
smallest of the group, the ratio of the presumed second phalanx to the humerus is
only 1.18. By contrast the ratios of the third
phalanx to the humerus in the specimens
mentioned above are 1.54,1.33+, and 1.30,
respectively; these values are significantly
higher,
g
. 3 r i ; -• -
d
New Material
(Buckland)
Postilla 189
*
Fig. 14
Dimorphodon macronyx, YPM 350, isolated
metapodials. a, 350 P, metatarsals ll-IV of right
pes, dorsal view; b. 350 I, metatarsals III and IV
of left pes, dorsal view; c. 350 L, metacarpal,
ventral view; d, 350 A, metacarpal ventral
view. Scale is in mm.
At least two segments of the wing-finger
are represented on the main slab of accession number 456 (YPM 350); they are the
complete second and contiguous third phalanges (YPM 350 D and C), and possibly
part of a fourth (YPM 350 K). The second
and third (Figs. 16b, c) are of typical form
and proportion for Dimorphodon; they articulate snugly, but are unfortunately flattened and yield no new information. The
same is true for YPM 9176 (Fig. 11 f), an
isolated, mostly complete second wingphalanx with a preserved length of 76 mm;
and YPM 9179 (Fig. 11 g)f a shattered third
wing-phalanx 101 mm long. The articular
ends of the wing-phalanges show the typical ovoid ball-and~cup arrangement: the
proximal facet of each phalanx is concave
and the distal end is convex. The shafts are
quite straight and there seems to have
been little movement possible between the
phalanges,
YPM 350 K (Fig. 12i) is an incomplete,
flattened, slightly tapering fragment ovoid
in cross-section. A faint impression on the
slab corresponds roughly to a further extension of the wider (proximal) end, about 5
mm away from it and continuing for a
New Material
(Buckland)
Fig. 15
Dimorphodon macronyx, YPM 350, obverse
views of isolated metapodials in Figure 14.
length of 10 mm. This evidence may support the identification of the bone fragment
as belonging to the fourth wing-phalanx,
since almost no other element of the skeleton would be so long, straight and slender,
There is no indication of an articular facet
at either end, A shallow fracture runs along
the exposed surface of the shaft as it does
in the other two wing-phalanges. The
width of the shaft supports the inference
that it comes from the distal half of the
fourth wing-phalanx, but it lacks the curvature that usually accompanies the tapering
of this element. The preserved bone is also
Postilla189
light and straight enough to belong to the
first phalanx of the odd fifth toe, and this
possibility must be considered,
From the few elements that are
preserved, the wingspan of these specimens can be roughly estimated, based on
the proportions of other Dimorphodon
material. The individual represented by
YPM 350 had a wingspan of about 1200
mm, while the wingspan of YPM 9178
would have been about 980 mm. The largest nearly complete specimen of
Dimorphodon (BMNH 41212) had a wingspan of almost 1450 mm.
The right femur (YPM 9182 G; Fig, 7e) is
bowed, but not sigmoid. Its length from the
tip of the head to the lateral condyle is 59
mm. The head is set off at an angle of about
22 Dimorphodon
macronyx
New Material
(Buckland)
Fig, 16
Dimorphodon macronyx, YPM 350, long
bones removed from matrix, a, 350 B, right
tibia-fibula, anterior view; b 350 D, second
wing-phalanx; c, 350 C, third wing-phalanx.
120° from the axis of the proximal region of
the shaft. The articular surface is rounded
and smooth; the neck is slightly constricted
but rather robust, much like the configuration in bipedal dinosaurs such as Coelurus
and Dilophosaurus. There is evidence of a
greater trochanter, although most of this
region is crushed. The distal end of the
femur curves slightly laterally and the lateral condyle extends slightly farther distaliy
than the medial, which is larger and more
pronounced. The expansion of the distal
condyles of the femur, in the t w o
Dimorphodon
specimens described here
and in all known pterosaurs, is mainly
subterminal. The articular surfaces of these
condyles are oriented 90° ventral to the
shaft axis.
The right tibia-fibula (YPM 9182 H: Fig.
7d) has been preserved adjacent to the
femur, and almost in natural position,
except that the tibia-fibula has been rotated
PostlIia189
to lie w i t h the anterior side down. Both
bones have been removed from the slab,
and their natural articulation can be determined (Fig. 17). It is evident that the medial
condyle of the femur articulated w i t h the
tibia, whereas the lateral condyle articulated w i t h the fibula, as Seeley (1901) stated,
contrary to Owen (1870:52). The tibia and
fibula of rhamphorhynchoids were fused at
their proximal ends. The tibia is convex and
the fibula concave at the surface where
they meet. YPM 350 B, a complete right
tibia-fibula (Fig, 16a), was preserved with
the anterior face up, unlike YPM 9182 H.
The entire proximal joint surface of YPM
350 B is well preserved, and slopes posteriorly at an angle nearly 50° to the long axis
of the shaft. The femur, therefore, did not
normally meet the tibia-fibula in columnar
fashion. However, a range of movement of
about 135° appears to have been possible
at the knee, and the femur and tibia-fibula
probably met at an angle of 7 5 - 9 0 ° in
normal stance, w i t h the femur more or less
horizontal and the tibia-fibula nearly
vertical, as in birds (Fig. 17).
There is no sign of a patella in any
pterosaur. An incipient expansion similar to
the cnemial crest of modern birds, but
New Material
(Buckland)
much less pronounced, has been noted in
specimens from the Cambridge Greensand
(Seeley 1901), and more recently by Galton
(1981 a). This tuberosity is present in
Dimorphodon as well, and, as Seeley
noted, it does not appear to represent a
separate center of ossification.
The reduction of the fibula in rhamphorhynchoids (Fig. 18a, b) resembles in
many respects the same pattern seen in
birds. YPM 9182 H (Fig. 7d) is a right tibiafibula 85 mm long. 7 mm from the proximal
end, the shafts of the tibia and fibula
separate, and continue for a length of 20
mm spaced by a distance of approximately
1 mm before fusing again. The line of fusion
is at least 12 mm long, and as the fibula
gradually tapers along this length its distal
extent becomes indistinguishable from the
tibia, partly as a result of crushing. The total
length of the fibula is thus at least 39 mm,
or approximately 46% of the tibia, in this
specimen. The other right tibia-fibula (YPM
350 B; Fig. 16a) in this collection is nearly
20 mm longer, but the proximal contact between tibia and fibula is only 5 mm, the interosseal space is at least 28 mm long, and
the distal fusion of the two bones appears
to extend for another 28 mm, although
crushing is again a problem. Like pterosaurs,
birds have an interosseal space between
the tibia and the fibula; the latter bone is reduced to a splint and usually merges into
the tibia at some distance before the distal
end.
The distal end of the right tibia-fibula
(Fig. 18c, d, e) is exceptionally well preserved in both YPM 350 B and YPM 9182 H.
This area, like the distal end of the humerus,
shows many remarkable similarities to the
homologous area of birds (Fig. 19). The
distal ends are comparable in the extent of
the anterior expansions of the bicondylar
surface that forms the joint. This distal expansion in pterosaurs has been taken to
represent the fusion of the proximal tarsal
elements (astragalus and calcaneum) with
the tibia, as in birds and small bipedal dinosaurs (Seeley 1901; Wellnhofer 1978). The
two condyles are of comparable size, but
Postilla 189
bird
pterosaur
Fig. 17
Comparison of the knee joints of the Golden
Eagle Aquila chrysaetos (above) and
Dimorphodon macronyx (below). In both, the
right femur and tibia-fibula are shown in lateral
(left) and anterior (right) views. Not drawn to
scale.
the lateral condyle is larger and rounder in
side view, while the medial condyle is
somewhat broader in anterior view. This
contrasts slightly with the situation in
birds, where both condyles are of approximately equal transverse width, but the lateral (external) condyle may extend farther,
and the groove between them is wider and
shallower than in pterosaurs (Currieand
Padian, in press). The ligamentous groove is
deep in pterosaurs, although not as deep as
in birds, and there is no bony supraligamentous bridge.
The distal tarsal elements preserved in
the two slabs (YPM 350 M and R and YPM
9182 I) are exceptional for the detail and
New Material
(Buckland)
Postilla189
\ i
a
N
'
•9»
i
u
1 cm
25 Dimorphodon
macronyx
New Material
(Buckland)
< Fig. 18
Dimorphodon macronyx. a, anterior views of
proximal ends of right tibiae-fibulae of YPM
9182 E (left) and YPM 350 B (right); b, posterior
views of the same; c, anterior views of distal
ends of right tibiae-fibulae of YPM 350 B (left)
and YPM 9182 E (right); d, posterior views of
the same; e, distal ends of tibiae: YPM 350 B
in lateral view (left), YPM 9182 E in anterior
view (right).
Fig. 19 V
Anterior views of distal ends of right tibiaefibulae of Dimorphodon macronyx (left) and
the Golden Eagle Aquila chrysaetos (right),
drawn to the same size. In both, astragalus
and calcaneum are indistinguishably fused to
the bases of the long bones. Abbreviations: br,
bony bridge of transverse ligament; condext,
external or lateral condyle; cond int, internal
or medial condyle; gr Edl, groove for M. Extensor digitorum longus; grPp, groove for M.
Peroneus profundus; inc, incisura; L, lateral
ligamentous prominence; L lo, lower attachment of Ligamentum obliquum; M, medial
ligamentous prominence; U lo, upper attachment of Ligamentum obliquum. Not drawn to
scale.
Postilla189
the information they yield about the pterosaurian ankle. These elements must be considered the lateral and medial tarsals, since
the astragalus and calcaneum are fused to
the tibia-fibula. YPM 350 M (Figs. 12c, 13c)
is the left lateral distal tarsal. YPM 350 R
(Figs. 12d, 13d) is the left medial distal
tarsal, and the t w o right tarsal elements are
preserved in their natural articulation w i t h
each other in the smaller specimen YPM
9182 I (Figs. 12h, 13h). The correspondence
of detail between these t w o specimens indicates that neither has suffered either
wear or distortion, although there is a break
in the flat, quadrangular medial distal tarsal
of YPM 9182 I, w h i c h has been repaired.
The lateral distal tarsal is a short stump
nearly 6 m m in length and roughly 2 m m in
cross-section, w i t h a complex topography.
The medial distal tarsal is a flat quadrangular plate 5 m m at the widest edge and 4
m m across, w i t h t w o raised ridges on its
distal face (Fig. 12d, h) that match the corresponding metatarsals, The surfaces of
these tarsal elements are finely porous,
w h i c h suggests a cartilaginous covering.
The tarsal unit is roughly wedge-shaped. It
thins anteriorly to a slight degree, but much
more so medially, especially on the distal
cond ext
cond int
bird
New Material
(Buckland)
surface. The distal view of these tarsals (Fig.
12d, e, h; Fig. 20) clearly shows the articular
facets for the metatarsals. The large aberrant fifth metatarsal articulates laterally and
slightly posteriorly with the lateral face of
the lateral tarsal. The other four metatarsals
are oriented normally. The articular surface
for the fourth metatarsal appears to be
shared by the lateral and medial tarsals,
while the third and second are carried entirely by the medial tarsal. There is no space
for the first metatarsal to articulate, which
is consistent with observations on other
pterosaurs (Wellnhofer 1978, Abb. 17).
The lateral distal tarsal corresponds in
both shape and topography to distal tarsal
4 of the lower Jurassic theropod dinosaur
Syntarsus (Raath 1969:19, his fig. 6b): "Its
proximal and medial surfaces are concave,
and its distal and lateral surfaces are
convex. The lateral surface also has a small
notch to accommodate the proximal end of
metatarsal V." In Syntarsus the lateral
distal tarsal is fused to the metatarsals, but
in theropods this element, when free, is usually identified as a fusion of distal tarsals 2
and 3 (Ostrom 1969) because it covers
metatarsals II and III, as the corresponding
element does in pterosaurs.
The proximal surfaces of the distal tarsals (Figs. 13d, e, h; 20) show very clearly
the rounded depressions which served as
the articular facets for the tibia. The larger
fossa is on the correspondingly wider
medial tarsal, because the medial condyle
of the tibia is the larger of the two. A tuberous posterior process of the lateral tarsal
partly overlaps the posterior face of the
medial tarsal, and may have been the site
for tendinous attachments of muscles that
extended the foot.
The metatarsal elements preserved on
this slab include metatarsals ll-IV of the
right pes (YPM 350 P: Figs. 14a, 15a) and
metatarsals III and IV of the left pes (YPM
350 I: Figs. 14b, 15b). The elements of both
are preserved in a coalesced state. The
proximal ends interlock and may have been
fused; metatarsals II and IV meet at the
dorsal surface near the proximal end of the
Postilla189
metatarsus, displacing metatarsal III ventrally to a slight degree. The distal ends of
the metatarsals are separated and splay
slightly/recalling the situation in birds and
some theropod dinosaurs (Osmolska 1981).
The two metatarsals of YPM 350 I are not
completely fused along their length, and
lack 5 mm at their distal ends, compared to
the complete members of YPM 350 P. The
third metatarsal is slightly longer (about 1
mm) than the second and fourth; the first,
when it is preserved, is about 1 mm shorter
than these (Owen 1870). A slight lateral curvature at both ends, and a gradual swelling
at the proximal end, identifies the fourth
metatarsal. There are ginglymal grooves on
the ventral and distal sides of the distal
ends of the metatarsals, which are not as
pronounced as in birds, but are comparable
to those of theropod dinosaurs. The first
four metatarsals seem to have functioned
as a unit; the toes flexed in the same plane
as the tarsus, and diverged distally to a
slight degree, as in birds. Two phalanges
(YPM 350 G and N) have been identified as
pedal, and were discussed earlier. No remains of the odd fifth digit, or of any other
phalanges or unguals, have been preserved
among these specimens. An extremely delicate metapodial (Fig. 4d) approximately 22
mm long but only 0.8 mm in diameter is
preserved in one corner of the slab of YPM
9182. From its uniform width and straightness it appears to be a metatarsal, but one
articular end is unfortunately missing and
there are no other metapodials preserved of
this specimen.
Fig. 20 •
Four views of the right distal tarsals of
Dimorphodon macronyx, reconstructed from
YPM 350 M and R and YPM 9182. The bottom
picture shows the facets for medial (left) and
lateral (right) condyles of the tibia, shown in
Figure 26. Scale = 1 mm.
New Material
ANT
distal
POST
PROX
posterior
DIST
DIST
anterior
PROX
ANT
proximal
POST
(Buckland)
Postilla189
New Material
(Buckland)
Postilla189
postcranial proportional differences* led
Wellnhofer (1978) and Wild (1978) to
place Eudimorphodon in a separate
Through the first half of the 19th century all family, the Eudimorphodontidae, and to
pterosaurs were classified as Pterodactylus, deny a strict phyletic connection to
Dimorphodon on the basis of the many
following the example of Cuvier. In 1846
derived characters of the former. Wild
von Meyer recognized the genus
(1978) suggested instead a closer relaRhamphorhynchus, but it was not until
tionship between Eudimorphodon
the turn of the century that Plieninger
and the later rhamphorhynchoid
(1901) established these two forms as
Campylognathoides, from the Upper Lias
representatives of separate suborders
of Germany. He based this view on several
within the Pterosauria. When Buckland
skull characteristics, the quadrangular
(1829, 1835) described the first pterosaur
form of the deltopectoral crest of the
specimen from Lyme Regis, at the time
humerus, the quadrangular sternal plate, '
the largest known representative of the
and the number and topology of the
Order, he accordingly identified the
carpal bones, which are variably ossified
genus as Pterodactylus and added the
and preserved in rhamphorhynchoids.
specific epithet macronyx ("large claw").
Peteinosaurus is smaller and known from
When a skull was finally found in 1858,
less complete material than Eudimorphodon,
however, it proved to be so different from
but is clearly a distinct taxon. No cranial
those of other pterosaurs that Owen immaterial is known but most of the lower
mediately erected a separate genus for it.
jaw has been preserved, and its dimorphoThe name Dimorphodon referred to the
dont dentition is also unique. The anterior
two types of teeth in the lower jaw: the
laniaries, of which there are an uncertain
"long, slender, trenchant and sharppointed laniaries" seen in other pterosaurs, number, are known only from impressions
on the counterslab of one of the two
followed posteriorly by a unique "series of
specimens. The posterior teeth, which
small, lancet-shaped, close-set teeth"
appear unicuspid, are small and close-set,
(Owen 1870: 42). A mysterious, isolated
but they point backward sharply, in condimorphodont jaw found some years eartrast to the simpler, smaller, peglike lanlier had been supposed by Owen to
cets of Dimorphodon. Wild (1978) sugbelong to a fish, contrary to Buckland's
gested that Peteinosaurus was ancestral
opinion that it actually pertained to the
to Dimorphodon and placed it in the
pterosaur of which Buckland had preDimorphodontidae Seeley 1870 on the
viously described postcranial remains.
basis of dental configuration and postcraThe presence of these two forms of
nial proportions.
teeth in the dentary, therefore, was the
principal autapomorphic feature defining
Assignment of the Yale specimens deDimorphodon as a distinct taxon. In the
scribed here to any known pterosaur taxon
past decade, however, two new pterosaur
is uncertain because of the absence of the
taxa with dimorphodont dentition were dis- lower jaw: no assessment of dimorphodoncovered in the Norian horizons of northern
ty can be made. However, the preserved
Italy. The first is Eudimorphodon ranzii
skull fragments correspond to those of the
Zambelli 1973; the second is Peteinosaurus two skulls of Dimorphodon in the British
zambellii Wild 1978. Eudimorphodon,
Museum (Natural History) (Owen 1870,
the larger of the two, had the basic plan
plates XVII and XVIII). Furthermore, the denof large anterior laniaries followed by
titions of the midmaxillary portions of these
smaller close-set teeth in the lower jaw,
skulls, while not recognized as diagnostic
except that the latter were variably 1 -, 3-,
for the genus, are topographically identical
or 5-cusped. These and other cranial and
and differ from those of Eudimorphodon
Referral of the Specimens to
Dimorphodon macronyx (Buckland)
New Material
(Buckland)
and Peteinosaurus. Compared to pterosaurian genera of the Upper Lias in England
and Germany, the maxillary portion is not
so deep as in Dorygnathus, the antorbital
fenestra is much shorter than in
Parapsicephalus, and the base of the orbit
is not rounded as in Campylognathoides.
However, the Yale material matches
Dimorphodon in all these respects. The
preserved portion of the skull at hand is not
preserved in Peteinosaurus, but the proportions of the postcranial material are
more similar to Dimorphodon than to
Peteinosaurus. These specimens also
come from the same Hettangian horizons
as the known specimens of Dimorphodon,
the only pterosaur from that area or stratigraphic level. This is not a good criterion of
taxonomic placement, but is strong circumstantial evidence. No pterosaur is reliably
reported from more than one stratigraphic
horizon, and geographically the genera are
highly endemic. On these bases there
seems to be adequate justification for assigning these specimens to Dimorphodon
macronyx.
Reconstruction of the Skull
The sutural connections of pterosaur skulls
are often obscured, and conflicting interpretations have resulted. Four reconstructions
of the skull of Dimorphodon are reproduced in Figure 5. Of these, Arthaber's is
perhaps most nearly correct in several important features, including the dentition,
the jugal, and parts of the lower jaw. He
shows that, while the posterior maxillary
teeth do become progressively smaller,
they do not become as fine or as numerous
as the lancet-shaped teeth of the lower jaw.
But the lower jaw is not as deep as Arthaber
figured it: most of what he, and probably
the other authors, perceived as the lower
posterior part of the left ramus is actually
both rami, compressed together and slightly displaced. Again, the configurations of
the bones of the roof and back of the skull
Postilla189
are hypothetical, since they are only partly
preserved in known specimens.
The reconstruction in Figure 6 attempts
to incorporate the preserved YPM skull
material into the general plan of the BMNH
skulls. YPM 9182 is considerably smaller
than YPM 350, and this is slightly smaller in
turn than the three specimens in the British
Museum, which are complete enough to
give some indication of total size.
Accordingly, the Yale specimens can be
considered juvenile, and the maxillary portion of YPM 9182 gives some insight into
juvenile characters of the skull that differ
from those of the adult form. This skull fragment is not congruent with those portions
of the two British Museum skulls. When
scaled upward isometrically, either the
upper jaw becomes too deep, or the width
of the preorbital opening becomes too
short. The juvenile form of the skull appears
to be relatively shorter and higher than the
adult form. As reconstructed, the ratio of
the length of this skull to its maximum
height is approximately 2.5. In the larger
British Museum skulls (41212, R 1035), the
length is at least three times the maximum
height. The restoration of the skull of YPM
9182 suggests a length of approximately
142 mm, about 55% of the larger British
Museum skulls, whereas the tibia (YPM
9182 H) is 65% of that of BMNH 41212 and
the humerus (YPM 9182 C) is 70% of the
same specimen. Thus, not only is the size
difference considerable, but different regions of the skeleton grow at different
rates. A similar tendency can be seen in
juveniles of Pterodactylus (Wellnhofer
1970) and birds, which have relatively
shorter, higher skulls than adult forms. This
appears to be generally true among
tetrapods.
The skull of Dimorphodon has sometimes been compared to a bicycle in
lightness, economy, and strength of construction in the strutlike facial bones. The
cranial vault and snout are not nearly so
high in later pterosaurs. The remarkable
lightness and delicacy of construction in
the pterosaur skull are evident even from
New Material
(Buckland)
Postilla189
the few fragments preserved in YPM 9182.
The thickness of the maxilla cannot have
exceeded a few millimeters, even in the
larger specimens of Dimorphodon. Its
structure consisted of two paper-thin laminar veneers separated by a spongiose layer
of cancellous bone, the whole structure
scarcely wider than the diameter of the largest teeth. When crushed, the laminar
layers around the larger teeth have often
been abraded away, and the alveoli
destroyed, which results in separation of
these teeth from the jaw. In life, however,
these must have been firmly anchored, as
the remaining teeth show (Fig. 4a). The construction of the pterosaur skeleton is testimony that the strength of a skeleton is not
dependent solely on the thickness of bone,
but rather on the interaction and arrangement of both hard and soft tissues in
response to the forces of stress most
frequently encountered by the animal.
Pterosaurs show how far the limits of reduction of hard tissues can be taken without sacrifice of essential functions. This observation has been explored in detail with regard
to the postcranial skeleton, particularly as it
relates to flight (Hankin and Watson 1914;
Bramwell and Whitfield 1974), but has
never been considered with regard to the
construction of the skull.
The only carpal element preserved in the
Yale material of Dimorphodon is the right
medial (usually called "lateral") carpal of
YPM 350 H (Figs. 12a, 13a). However, it has
not been generally appreciated that most of
the elements of both wrists are preserved
in the type specimen of Dimorphodon
(BMNH R 1034). The left wrist is in place,
but partly obscured by the overlying first
wing-phalanx. This specimen was recently
damaged when the collections were
moved to the new wing of the British
Museum (Natural History), and the
metacarpal-phalangeal region shattered.
The proximal end of the pteroid, identified
by Owen (1870:44, as "styloid"), is now
broken off. Of the right wrist, the proximal
carpals are represented by the piece
marked j in Buckland's (1835) plate (Fig.
21). This piece, along with bones marked k
and /, Buckland included in the right
carpus, k is the medial carpal, identical to
YPM 350 H, but /is a lateral distal tarsal. A
small sliver of bone in the same area of the
slab, labeled by Buckland e, was identified
as a rib, but it is in fact the right pteroid
bone and its supporting sesamoid base.
Owen did not identify this bone, but he
claimed to find both pteroids in the jumble
of wing bones that covers the back of the
skull of BMNH R 1035. He did not, however,
indicate themin his plate, and I have been
unable to verify his identification. Neither
pteroid is clearly visible in BMNH 41212.
Identification of Small Bones in the
British Museum Dimorphodon
Specimens
Wild (1978) described for the first time
small sesamoid bones dorsal to the distal
The importance of the Peabody Museum
specimens of Dimorphodon is that they
are largely uncrushed. Some bones, like the
humerus, are better preserved than in any
other specimens of Dimorphodon; other
bones, like the distal tarsals, can be studied
for the first time. Reference to the specimens of Dimorphodon in the British
Museum (Natural History) helps to identify
previously unrecognized elements among
the latter material, including carpal and
tarsal bones.
Fig. 21 •
The type specimen of Dimorphodon macronyx
(BMNH R 1034), as illustrated by Buckland
(1835, plate XXVII). Buckland did not realize
that the features labeled 3"and /in his figure 1
belonged to the same bone (the wingmetacarpal), and therefore his reconstruction
of the wing in figure 2 is missing a joint at the
wrist. The jaw shown in figure 3 was not associated with other material; Buckland guessed
correctly that it pertained to the pterosaur he
had first described in 1829.
New Material
(Buckland)
Postilla189
New Material
(Buckland)
ends of the penultimate phalanges of the
hand of Eudimorphodon. It should be
noted here, in light of this most interesting
discovery, that these elements have also
been preserved in Dimorphodon. In the
type specimen (BMNH R 1034) there is one
behind the third claw of the left hand, while
in BMNH 41212 they are visible behind the
claws of the first and second digits of the
right hand (Fig. 22). Dr. Wild (personal
communication) has since recorded antungual sesamoids in a Dorygnathus specimen in the collections of the Institut fur
I Palaontologie und historische Geologie in
Tubingen, a finding I can confirm from
casts sent to me by Dr. Frank Westphal. I
Postilla189
have been unable, however, to find evidence of them behind the claws of the foot
in Dimorphodon (BMNH 41212) or any
other pterosaur.
Fig. 22
Detail of Dimorphodon macronyx, BMNH
41212, showing right manus and left pes, the
latter in plantar view. Abbreviations: Idt, lateral
distal tarsal; It left tibia; mc, metacarpal; mdt,
medial distal tarsal; mt, metatarsal; rt, right
tibia; ses, sesamoid; wph, wing-phalanx.
Large Roman numberals designate phalanges,
except for wing-phalanges. Scale = 1 cm.
New Material
(Buckland)
Postilla189
Articulations and Function of the
Forelimb
The fine preservation of many prominences
and articular surfaces in the Yale material is
crucial to the interpretation of functional
morphology of the appendicular skeleton of
Dimorphodon. From these remains, certain
hypotheses about how pterosaurs walked
and flew may be presented for the first
time, subject to corroboration by comparative functional anatomy and aerodynamic
requirements.
YPM 350 F, the right humerus described
earlier, is probably the best-preserved bone
of this kind among pterosaurs. Several notable features have been clarified, especially
the pronounced torsion of the shaft, the
ridges showing attachments of muscles
along the shaft, and the features of the
distal end, particularly in palmar view.
The movement of the humerus cannot
be understood without reference to the pectoral girdle. Pectoral elements are absent
from the Yale Dimorphodon material, and
the sternum is not recorded in any
specimen. The bones Buckland (1835) took
for the sternal plate in BMNH R 1034 are
cervical vertebrae. However, a wellpreserved platelike sternum is known in the
earlier pterosaur Eudimorphodon, from the
Norian of Italy (Zambelli 1973, Wild 1978),
and in all later forms; so there is no reason
to doubt its presence in Dimorphodon. The
pectoral girdle in Dimorphodon (BMNH
41212) is of typical form and extremely
birdlike (Fig. 23). The coracoid is elongated
and stout, and is fused to the bladelike, attenuated scapula. It has a prominent process similar to the acrocoracoid of birds
located anterior to the glenoid fossa, which
is bounded anteriorly and posteriorly by
raised bony knobs. These served as the site
of origin for several forelimb muscles, and
restricted the humerus from slipping out of
its socket. The concave, saddle-shaped
head of the humerus otherwise moved
freely, and was capable of being retracted
against the body to fold the wing as in
birds. This action was further supplemented
Fig. 23
Right pectoral girdles in lateral view. Above,
Dimorphodon; below, Aquila chrysaetos.
Abbreviations: a, acrocoracoid process; c.
coracoid; £furcula; s, scapula. Scale bar =
1 cm.
by flexion of the elbow and metacarpalphalangeal joints.
The primary action of the humerus was
in the flight stroke. The mechanics of the
flight stroke can be approached in three
ways: (1) joint mobility and articular
limitations; (2) comparative functional analysis with other flying vertebrates; and (3)
aerodynamic requirements for flight, to
which the flight apparatus must conform.
New Material
(Buckland)
Postilla189
Only the first approach will be considered
here.
It was stated above that the humerus
could be fully retracted to close the wing
against the body. It could be protracted approximately 90°, or to the point where the
axis of the shaft would be perpendicular to
the plane of the glenoid fossa (Fig. 24). Further protraction was prevented by the bony
knob anterior to the glenoid fossa. The
humerus could also have been raised and
lowered through an arc of approximately
90°.
Because radius and ulna are not suitably
preserved in any rhamphorhynchoid pterosaur described thus far, the limitations of
movement at the elbow can only be
estimated. The elbow is a hinge joint that
corresponds in mechanical detail quite
closely to the elbow of birds. The similarities
of the processes and areas of muscular attachment at the distal end of the humerus
have already been noted (Fig. 10c). A mobil- Fig. 24
Right pectoral girdle and articulated humerus
ity approximately equivalent to that of
of Dimorphodon. Above, in retracted position;
birds, i.e., somewhat less than 180°, can be
below, protracted as in flight. Note downfairly assumed. The joint separating the
and-forward
rotation of humerus during flight
fourth metacarpal and wing-finger is a
stroke. Scale = 1 cm.
hinge joint of great mobility, very similar to
the outer joint of the bird wing (Bramwell
and Whitfield 1974). The principal structur- turbed articulated specimens, in which the
al difference, of course, is that this joint is
wing-finger always forms a taut, bowlike
the carpometacarpal in birds, whereas in
structure. Hence, the majority of movement
pterosaurs it is the metacarpophalangeal
in the wing occurred at three joints: the
joint of the fourth (wing) finger (Fig. 25).
shoulder, the elbow, and the base of the
This articulation is well preserved in several fourth finger. The first had a wide range of
BMNH specimens, though not in the Yale
movement in several planes, while the
material. In Dimorphodon there is some
second and third were simple hinges with
slight movement possible between the zeu- extensive mobility in only one plane. It is
gopodials and the proximal carpal, and beevident that the wings of birds and pterotween the distal carpal and the metacarpals, saurs are divided into equivalent functional
but the proximal and distal carpals interlock units, analogous in a mechanical sense but
snugly. It is difficult to assess the amount of not homologous in structure.
movement between the phalanges of the
It is curious that in rhamphorhynchoid
wing-finger. These joints are flattened ballpterosaurs, as in theropods, the phalanges
and-cup articulations, never anchylosed
of the manus are generally more robust
but also without clearly developed collaterthan those of the pes, and the claws are
al ligament fossae or any other evidence of
larger and more trenchant (Fig. 22). Larger
restricted motion. The only indication that
theropods often tended to reduce the
movement was restricted between these
forelimbs, while pterosaurs enlarged them.
phalanges comes from relatively undisIt is possible that the first three digits of the
New Material
(Buckland)
Postilla189
tween the branches of trees. Of these, none
can be logically excluded, but there is no
direct evidence for any. Pterosaurs were
not necessarily arboreal, but they were
predators. I would suggest that a function
in predation is more likely than climbing or
hanging. It should be remembered, though,
that flight was the primary function of the
forelimbs. No movement that contradicted
the requirements of joint mobility and articulation for the flight stroke would have
been possible: this seems to be the only
caution.
Fig. 25
Comparison of the right forelimb skeletons of a
generalized rhamphorhynchoid pterosaur
(above) and a bird (below); only the proximal
Articulations and Function of the
portion of the pterosaur's first wing-phalanx is
shown. Abbreviations: c, carpus; h, humerus; Hindiimb
mc, metacarpus; pi pteroid; r, radius; u, ulna.
I—IV, digits.
The hindiimb of Dimorphodon is better preserved in the Yale specimens than in any
other early pterosaur, and allows considerapterosaur hand were enlarged mainly as a
ble insight into the stance and gait of the
developmental consequence of the hylimb as well as particulars of its kinematics.
pertrophy of the fourth finger. Only the phaNo pelvic bones are preserved, however.
langes of the first three digits were
These are known from the BMNH specimovable, because the first three metacarmens and are of more or less standard ptepals were appressed and bound, probably
rosaurian type. The ilium is low and
ligamentously, to the fourth. But the wellbladelike, with rodlike processes anteriorly
developed flexor tubercles of the
phalanges, especially the claws, seem to in- and posteriorly. The acetabulum is
imperforate, and ilium, ischium, and pubis
dicate considerable movement was
seem to contribute to it. The ischium and
possible. Ginglymal grooves are deep and
pubis are fused in a continuation of the
allow a wide range of flexion and
platelike form seen in the ilium. Most of this
extension; one is reminded on examination
broad expansion is generally identified as
of the unguals that Buckland did not idly
the ischium, with the pubis consisting of a
name this species macronyx. The enorvertical, stalklike element incorporated into
mous flexor tubercles of the claws suggest
the pelvic plate. The two separate stalks of
strong powers of grasping, perhaps in
climbing, but equally possible for manipula- the pubis were joined medially by a paired
element regarded as the prepubis. Its form
tion or gouging, perhaps in predation. A
is variable in pterosaurs: it is rodlike and
common function of sesamoid bones in
divided distally in Rhamphorhynchus
such situations is to sustain tensile forces
(Wellnhofer 1975), but in earlier forms it is
around the extensor site of a joint where
flatter and roughly spatulate, with a
much flexion occurs (Hildebrand 1974),
diamond-shaped median blade in place of
and this would be expected in cases where
the prepubic "prongs" seen later in
flexion is indicated by such well-developed
Rhamphorhynchus. The edges of these
ungual tubercles. If so, it can be suggested
blades are irregular and rugose, and sugthat some type of grasping function was
highly probable. In the past, suggested uses gest extensive cartilaginous attachment as
in the pelvis of crocodiles. Pterosaurs
of these digits have included grooming,
feeding, hanging from cliffs, and moving be- lacked a mammalian diaphragm, but it is
New Material
(Buckland)
possible that the prepubis in pterosaurs
served as the origin of a muscle similar to
the M. diaphragmaticus of the crocodile,
which via its insertion on the liver acts as a
piston mechanism for inspiration by pulling
air into the lungs (Gans and Clark 1976). In
flight, respiration may have been accomplished in part by expansion and contraction of the chest along with the flight
stroke. These suggestions, however, are
offered only by analogy with birds and
crocodiles.
The puboischiadic plates were fused to
some extent along their ventral borders.
This statement is contrary to the traditional
view (Wellnhofer 1970,1975,1978), but
there are notable examples in which the
median synthesis has been preserved.
These include the Carnegie Museum specimen of Campylognathoides liasicus, the
type specimen of C. zittelim the Staatliches Museum fur Naturkunde Stuttgart,
and a slightly distorted but otherwise fully
articulated and uncrushed pelvis oiPteranodon in the Peabody Museum (Eaton
1910, plates X and XI). The consequence of
this arrangement is that the acetabulum is
made to face downward and outward, not
upward and slightly backward as in Wellnhofer's reconstructions (Padian 1980).
The rest of the pterosaur hindlimb is
functionally analogous to bipedal dinosaurs
and birds, not to bats or other arboreal
mammals as traditional reconstructions
imply. It will be recalled that the head of the
femur is set off to the side of the main axis
of the shaft, not central to the shaft as in
bats. This limits movement of the femur to
protraction and retraction in a nearly parasagittal plane. The orientation of the distal
articular surfaces with respect to the axis of
the femoral shaft indicates that the articulation of the femur with the tibia and fibula
was normally much closer to a right angle
than a straight line, when viewed from the
side. The knee joint was, therefore, a hinge
allowing no significant rotation during
normal locomotion. Schaeffer (1941) observed that a well-offset femoral head corresponds to the role of the tibia as the main
Postilla189
bearer of weight, and went on to suggest
that the movement of the pterosaur hindlimb must have been largely restricted to
the parasagittal plane, as in birds. This
agrees with the idea that a large medial
condyle is a primary indicator of parasagittal locomotion (D. Brinkman, personal
communication.) The length of the fibula is
variable in proportion to the tibia in both
birds and pterosaurs, and this is to be expected of an element that is so reduced in
size and function. The expected position of
the tibia would be more or less vertical
when the animal was at rest. In motion, the
tibia would have swung through a wide
parasagittal arc while the femur remained
in a more horizontal position. The motion of
the distal end of the femur would have
been more up-and-down than backand-forth, like the knees of birds but unlike
the knees of humans.
The tarsal region of pterosaurs, detailed
here for the first time, demonstrates the
movements within the ankle region. The
proximal tarsal bones (astragalus and
calcaneum) can only be fused to the tibiafibula, as they are here and in birds and
theropods, when there is no movement between these limb elements. The formation
of a highly developed double condylar joint
emphasizes the restriction of motion to a
fore-and-aft plane, and the distal tarsals
show clearly on their proximal faces the depressions that receive the medial and lateral
condyles of the tibiotarsus. The distal end
of the tibiotarsus has many topographic
features that correspond to insertions and
grooves for tendons and ligaments of the
main flexor and extensor muscles of the
avian foot (see Fig. 19). The distal end is expanded anteriorly in birds, bipedal
dinosaurs, and pterosaurs, not distally as in
sprawling forms. This shows that the axes
of the tibia and the elongated metatarsals,
as viewed from the lateral side, did not form
a stright line but a sharp angle. Most flexion
and extension of the distal tarsals and metatarsals against the tibiotarsus occurred
within a range of about 90°to 150°, approximating the range in birds.
New Material
(Buckland)
The distal tarsals preserved in the Yale
Dimorphodon material also provide greater
insight than before possible into the articulations of the distal tarsal elements with
the metatarsals (Fig. 26). On their distal
faces a series of grooves mark where the
distal tarsals receive metatarsals ll-IV, the
fifth offset sharply in a distinct, diagonally
placed channel of its own. As with the knee
and tibiotarsal joints, there was little possibility of rotation here.
The entire ankle assembly is less rigidly
constructed than those of birds in the
sense that the latter group has more fusion
and definition of bony elements that form
the articulations of the ankle. However, soft
tissues such as cartilage, tendons, and ligaments still play an extensive part in the
function of the avian foot, as Cracraft
(1971) has shown. This situation in pterosaurs compares favorably with that of theropod dinosaurs, where, although some
fusion of the metatarsals may occur, the
distal tarsals are poorly defined when compared to the pterosaur's (see Ostrom 1969
for comparison with Deinonychus).
Therefore, because rotation at the ankle is
not assumed to have been a significant
component of gait in theropods, it is unlikely to have been important in pterosaurs.
The pterosaurian tarsal bones do not bind
the joint rigidly, but suggest strongly from
their features that the normal range and
extent of motion was primarily parasagittal,
like the movement of the knee. The pterosaurian ankle is properly regarded as
mesotarsal, as in birds and dinosaurs,
because the primary flexion is between
proximal and distal tarsals and there is no
movement between the proximal tarsals.
The function of the fifth metatarsal and
its long, aberrant toe remains a mystery, although it seems clear that digit V did not
operate like the other digits. Wild (1978)
has suggested the idea of stretching a web
of skin between digits IV and V for paddling
through the water, by analogy with a possible function in the foot of the Triassic
marine reptile Tanystropheus (Wild 1973).
This is certainly a possibility, although the
Postilla189
variable form of this digit in rhamphorhynchoids and its eventual loss in pterodactyloids (Wellnhofer 1978, Abb. 17) should
also be considered. The fifth metatarsal,
which is not preserved in the Yale specimens but which is well shown in BMNH
41212, has a variety of prominences and
tuberosities indicative of complex motion.
An especially well-marked groove, for
instance, is located on the plantar surface
between two pronounced tuberosities. Tendons running along this groove evidently inserted on a rugose prominence at the distal
end, and would have produced strong flexion of this digit (Fig. 26). The function of
digit V in posture and locomotion, whether
terrestrial or aquatic, is still not established,
but the fifth metatarsal of Dimorphodon is
the largest known among pterosaurs (in
Campylognathoides it is also quite large;
in Eudimorphodon it is unknown), and its
robustness in these early forms may indicate a primitive function that was reduced
or lost in later rhamphorhynchoids.
The ginglymal grooves of the distal ends
of metatarsals ll-IV describe an arc that
begins approximately in line with the axis
of the metatarsal shafts and continues between the ginglymal condyles to the shaft
axis (Fig. 27). This is comparable to the condition in birds and dinosaurs and unlike the
condition in crocodiles, lizards, and turtles.
The latter reptiles are plantigrade and normally do not walk with a great deal of flexion between metatarsals and phalanges. In
these groups the distal ends are normally
not bicondylar and the joint facets are
terminal, not subterminal. Nor in these
groups do the metatarsals function as a
coalesced unit, as they do in birds and
dinosaurs, and pterosaurs. Instead, as Brinkman (1980) has shown for the caiman, each
metatarsal lifts in sequence (I—IV) and the
main extension and flexion of the foot
occurs at the ankle. In pterosaurs a great
deal of flexion occurred at the phalangeal
joints, as their ginglymal facets show, because the metatarsus was raised off the
ground as it is in birds and theropods. The
main axis of support of the hindlimb, then,
New Material
(Buckland)
Fig. 26
Right ankle assembly of Dimorphodon
macronyx. The tibia and metatarsals are
shown in anterior view. Spaces for the reception of metatarsals ll-IV are indicated. Scale =
1 mm.
Post ilia 189
New Material
CD
b
_^J
(Buckland)
\fj
Q3 z$ f f
Postilla189
was through the two distal condyles of the
tibiotarsus, through the two distal tarsals to
the second, third, and fourth metatarsals
(Fig. 28). These properties suggest quite
strongly that pterosaurs were not plantigrade walkers, but digitigrade, contrary to
Wellnhofer's (1978) conclusions. No features suggest a plantigrade mode of
locomotion. Furthermore, all available evidence speaks for a completely upright,
parasagittal stance and gait in Dimorphodon and all other pterosaurs. In all skeletal
features that reflect the mechanics of limb
movement, pterosaurs agree with birds and
bipedal dinosaurs, not with crocodiles,
thecodonts, or any sprawling reptiles.
Reconstruction of Dimorphodon
Fig. 27 A
Distal ends of metatarsals in distal (left), lateral
(center), and plantar (right) views, a, turtle; b,
caiman; ctheropod dinosaur; d, Dimorphodon
macronyx; e, tarsometatarsus of a bird.
Arrows indicate the limits of the ginglymal
grooves. Not drawn to scale.
Fig. 28 T
Right pelvis and hindlimb of Dimorphodon
macronyx, restored in erect position, slightly
extended, in lateral view. Scale — 5 cm.
The skeletal reconstruction of Dimorphodon
given in Figure 29 reflects the conclusions
of this work. When the actual articulations
and possible actions of the bones comprising the appendicular skeleton are
examined, the traditional picture of pterosaurs as clumsy quadrupeds does not make
sense. Pterosaurs had well defined joints in
the limbs, and their movements can be
reconstructed with a high degree of
confidence. The mechanics of these joints
cannot be compared with those of
crocodiles, thecodonts, or living reptiles,
but in many cases are virtually indistinguishable from those of birds and bipedal
dinosaurs, as the preceding analysis has
shown. Some articular surfaces, like the
head of the humerus, the area of the wrist
and hand, and the distal tarsals, are not precisely like those of any known animals, although functionally analogous. Even so,
these joints are all well defined enough to
allow a confident approximation of the direction and range of their movement, and
in every case are functionally analogous to
the corresponding joints in birds or
dinosaurs.
Dimorphodon has been restored in
Figure 30 as a rapidly moving terrestrial
biped. The hindlimbs were apparently quite
Postilla189
CD
Q.
X2
C
O
E
o II
o CD
*2s CM
+->
c:
o
CD
O
13 in
C)
rphodon macr
ssio
kullab
abo
20 cm
(Buckland)
GO T—
r
o
.fc=
-J
CD c
CO CD
O Q.
CO
O)
^ (>
o
o
o 2
N O
ri> co
rrest rial
win
New Material
j£
CD
CO
.11.
2 DC
CD ~0
C!)
rCD
c
Fig. 30
Life-restoration of Dimorphodon macronyx, by
J. Kevin Ramos. Wing configuration inferred
from Rhamphorhynchus; "furry" covering
from Sordes pilosus. The horny covering
shown on the rostral area is based on an inference by Wellnhofer (1975) regarding
Rhamphorh ynchus.
New Material
(Buckland)
adequate to support the body without the
aid of the forelimbs. In fact, the forelimbs
could not have "walked" in the typical reptilian manner because of limitations on the
rotational and protractional capabilities of
the humerus, and the fact that the elbow is
a simple hinge. The proportions of the hindlimb of Dimorphodon and all other pterosaurs are unusual among reptiles: the metatarsals are elongated, and the tibia is appreciably longer than the femur. This situation is found in no thecodonts except
Lagerpeton, Lagosuchus, and
Scleromochlus, and in no crocodiles, but is
characteristic of small bipedal dinosaurs
and birds. These proportions are assumed
to correlate with agility, rapid movement,
and possible cursoriality (Coombs 1978),
and are certainly typical only of advanced
archosaurs.
Acknowledgments
It is my great pleasure to thank Dr. A. J.
Charig of the British Museum (Natural
History) for his kind permission to study,
photograph, and refer to specimens in his
care. For their cooperation and help I am indebted to the preparators and staff of the
Post ilia 189
British Museum (Natural History), including
Ron Croucher, Sandra Chapman, and Cyril
A. Walker. It is also a pleasure to acknowledge the achievement of Rebekah Smith,
who prepared the fragile specimens in the
Peabody Museum by hand; Mary Ann
Turner, for her incomparable sleuthing of
the Peabody Museum records; and the
staff of Manuscripts and Archives, Sterling
Memorial Library, Yale University, for
access to Marsh's correspondence. Advice,
help, and facilities for the photographs in
this paper were provided by Professor
David E. Schindel of the Division of Invertebrate Paleontology at the Peabody
Museum, and Paul Morris provided
darkroom help. Previous drafts of the
manuscript were greatly improved by the
suggestions of Professors Bruce H. Tiffney,
J. David Archibald, John H. Ostrom, and
David E. Schindel. Finally, my deepest
thanks are due to Professors Keith S. Thomson and John H. Ostrom for allowing me to
describe the Yale material, and for all their
helpful discussion. This work was supported by the National Science Foundation
(Grant No. DEB-780211) and by a Yale University Graduate Fellowship, and is based
on part of a Ph. D. dissertation at Yale
University.
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The Author
K e v i n Padian, Department of
Paleontology, University of California,
Berkeley, CA 94720.

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